1. Field of the Invention
This invention relates to the detection of surface oxidation on metallic materials. More particularly, this invention relates to a method for detecting surface oxidation on titanium aluminide (Ti.sub.3 Al) material.
2. Description of the Related Art
Oxidation of a surface of a metallic material lowers the material's mechanical properties and can result in catastrophic failure. Detection of oxidation can be determined by etching the surface. However, current chemical etch solutions/methods do not reveal oxidized surfaces on titanium aluminide materials.
U.S. Pat. No. 3,518,133, issued to W. B. Glendinning, entitled "Method for Measuring the Thickness of a Diffused Surface Layer", discloses a method for measuring the thickness of a diffused surface layer on a silicon semiconductor substrate. The Glendinning method is a multi-step method including exposing the diffused surface layer to a fine jet of corrosive vapors of hydrogen fluoride and nitrous oxide to produce a corroded portion through the diffused surface layer; washing the corroded portion out of that layer with an alkaline solution; re-exposing a layer which extends through the diffused surface layer to corrosive vapors covering the layer with an optical flat; exposing the crater and flat to monochromatic light; and counting the interference rings thus created. The Glendinning method involves removal of the diffused surface layer without a determination of the depth of the oxidized layer. Thus, the thickness of the end product cannot be adequately controlled.
U.S. Pat. No. 4,698,130, issued to J. E. Restall et al, entitled "Cleaning of Metal Articles", discloses a halide based process for the removal of surface oxidation and corrosion contamination from metallic articles especially cracked superalloy turbine components. The process utilizes a pulsed pressure cycle utilizing CHF.sub.3 hydrogen and inert gas as atmosphere. The process is also applicable to etching for detection of near-surface flaws. The Restall et al method involves removal of surface contamination without detection or determination of the oxidized layer depth.
U.S. Pat. No. 4,282,266, issued to A. W. Fisher, entitled "Method for Determining Silicon Content in Layers of Aluminum and Silicon", provides a method for determining the silicon content in an aluminum film on a substrate. The substrate is immersion plated in a solution comprising the deionized water, hydrofluoric acid, and copper sulfate which plate onto the silicon in the film while etching the aluminum film. The substrate is then removed from the solution and the aluminum film visually examined to determine whether the areas plated thereon are continuous or discontinuous.